help: teach topic symbols how to dedent

When using docstrings for documenting symbols such as revsets,
templates, or hgweb commands, documentation likely has leading
whitespace corresponding to the indentation from the Python source
file.

Up until this point, the help system stripped all leading and
trailing whitespace and replaced it with 2 spaces of leading
whitespace. There were a few bad side-effects. First, sections
could not be used in docstrings because they would be indented
and the rst parser would fail to parse them as sections. Also,
any rst elements that required indentation would lose their
indentation, again causing them to be parsed and rendered
incorrectly.

In this patch, we teach the topic symbols system how to dedent
text properly. I argue this mode should be enabled by default.
However, I stopped short of changing that because it would cause
a lot of documentation reformatting to occur. I'm not sure if
people are relying on or wanting indentation. So, dedenting has
only been turned on for hgweb symbols. This decision should be
scrutinized.

mercurial/help.py

@@ -6,7 +6,7 b''
 # GNU General Public License version 2 or any later version.
 
 from i18n import gettext, _
-import itertools, os
+import itertools, os, textwrap
 import error
 import extensions, revset, fileset, templatekw, templatefilters, filemerge
 import encoding, util, minirst
@@ -172,7 +172,7 b' helphooks = {}'
 def addtopichook(topic, rewriter):
     helphooks.setdefault(topic, []).append(rewriter)
 
-def makeitemsdoc(topic, doc, marker, items):
+def makeitemsdoc(topic, doc, marker, items, dedent=False):
     """Extract docstring from the items key to function mapping, build a
     .single documentation block and use it to overwrite the marker in doc
     """
@@ -182,20 +182,25 b' def makeitemsdoc(topic, doc, marker, ite'
         if not text:
             continue
         text = gettext(text)
+        if dedent:
+            text = textwrap.dedent(text)
         lines = text.splitlines()
         doclines = [(lines[0])]
         for l in lines[1:]:
             # Stop once we find some Python doctest
             if l.strip().startswith('>>>'):
                 break
-            doclines.append('  ' + l.strip())
+            if dedent:
+                doclines.append(l.rstrip())
+            else:
+                doclines.append('  ' + l.strip())
         entries.append('\n'.join(doclines))
     entries = '\n\n'.join(entries)
     return doc.replace(marker, entries)
 
-def addtopicsymbols(topic, marker, symbols):
+def addtopicsymbols(topic, marker, symbols, dedent=False):
     def add(topic, doc):
-        return makeitemsdoc(topic, doc, marker, symbols)
+        return makeitemsdoc(topic, doc, marker, symbols, dedent=dedent)
     addtopichook(topic, add)
 
 addtopicsymbols('filesets', '.. predicatesmarker', fileset.symbols)
@@ -203,7 +208,8 b" addtopicsymbols('merge-tools', '.. inter"
 addtopicsymbols('revsets', '.. predicatesmarker', revset.symbols)
 addtopicsymbols('templates', '.. keywordsmarker', templatekw.dockeywords)
 addtopicsymbols('templates', '.. filtersmarker', templatefilters.filters)
-addtopicsymbols('hgweb', '.. webcommandsmarker', webcommands.commands)
+addtopicsymbols('hgweb', '.. webcommandsmarker', webcommands.commands,
+                dedent=True)
 
 def help_(ui, name, unknowncmd=False, full=True, **opts):
     '''